The trend in electronic circuits continues to be miniaturization and the performance of an increasingly large number of operations per unit of time. The typical state-of-the-art electronic circuit has numerous integrated circuits disposed on multiple semiconductor chips. Present semiconductor chips process information sufficiently fast such that the overall rate is limited primarily by the speed of the interconnecting conductors.
A Multichip Module (MCM) is a device interconnecting two or more semiconductor chips on a common substrate using extremely short conductors which function only as conducting interconnects. Since the conductors are extremely short, less delay time is encountered in the transmission of an electric signal from one end to the other. The extremely short conductors on the MCM substrate enable higher conductor densities and a smaller package size. Thus, MCMs provide excellent high-speed interconnection for high-performance digital electronic circuits in wireless products such as pagers, cellular phones, wireless modems, televisions, etc. Passive electrical components such as capacitors, resistors, inductors and the like, are embedded on the MCM substrate to provide circuits with various functionalities for matching, decoupling, coupling, and resonance.
A major problem associated with present MCMs is in the design of existing embedded resonators. A resonator is a critical electrical component in bandpass filters, oscillators, voltage-controlled oscillators, image rejection circuits, and other circuits requiring a high impedance at a desired frequency for a given purpose. The efficiency of such circuits require resonators with high quality factors.
Existing MCMs include resonators fabricated from a separate embedded inductor and a separate embedded capacitor, connected in series or in parallel (LC resonators). Other existing MCMs include resonators fabricated from a transmission line structure. MCMs including such resonators have many disadvantages. MCMs including LC resonators occupy more MCM substrate space thereby increasing the size requirements of the MCM. Further, LC resonators using two separate components, exhibit degraded quality factors and, the small capacitance required in the resonator is difficult to precisely achieve using the low-cost silicon fabrication processes. Consequently, the MCMs produced by these processes often result in low yields and poor quality.
If a high quality factor LC resonator is required in existing MCMs, the resonator is typically built off the chip, which increases the number and complexity of the input-output connection design of the resonator package for the chip, and causes spurious resonance from the parasitics of the packaging. MCMs having resonators implemented with transmission lines are not practical for wireless applications because of the high frequencies involved which range between 500MHz-3GHz. Such distributed circuits would require very long conductor lines to achieve the same order as the wavelength. Consequently, MCMs with conventional distributed resonators cannot be used in the circuits for wireless applications.
Studies on MCMs having embedded inductors fabricated on high resistivity silicon have shown that by careful design, the inductor can achieve a high quality factor. Previously, the design goal of a good inductor was to lift the self-resonant frequency well above the working frequency so as to maintain the lumped property. However, parasitic capacitance is almost intrinsic since present technology limits the ability to reduce such effects. By keeping the self-resonant frequency well above the working frequency, the inductance to be achieved has an upper limit.
Accordingly, there is a need for an improved MCM including a high quality factor resonator which avoids the disadvantages of prior art MCMs.